The Mendocino Complex Fire was a large complex of wildfires that burned in northern California for more than three months in 2018. It consisted of two wildfires, the River Fire and Ranch Fire, which burned in Mendocino, Lake, Colusa, and Glenn Counties in the U.S. State of California, with the Ranch Fire being California's single-largest recorded wildfire at the time until the Dixie Fire in 2021. The Ranch Fire burned eight miles northeast of Ukiah, and the River Fire burned six miles north of Hopland, to the south of the larger Ranch Fire. First reported on July 27, 2018, both fires burned a combined total of 459,123 acres (1,858 km2), before they were collectively 100% contained on September 18, though hotspots persisted until the complex was fully brought under control on January 4, 2019. The Ranch Fire alone burned 410,203 acres (1,660 km2), making it the largest wildfire in modern California history at the time until the August Complex fire that occurred in 2020. The Ranch Fire also surpassed the size of the 315,577-acre Rush Fire, which burned across California and Nevada, as well as the Santiago Canyon Fire of 1889, which was previously believed to have been California's all-time largest wildfire.

The Thomas Fire was a massive wildfire that affected Ventura and Santa Barbara Counties, and one of multiple wildfires that ignited in southern California in December 2017. It burned approximately 281,893 acres before being fully contained on January 12, 2018, making it the largest wildfire in modern California history at the time. It was surpassed by the Ranch Fire, part of the Mendocino Complex, in August 2018. The fire is currently the seventh-largest wildfire in modern California history, as of 2021. The fire was officially declared out on June 1, 2018, after more than two months in which no hotspots were detected. The Thomas Fire destroyed at least 1,063 structures, while damaging 280 others; and the fire caused over $2.2 billion in damages, including $230 million in suppression costs, becoming the seventh-most destructive wildfire in state history at the time. As of August 2020, the Thomas Fire is California's tenth-most destructive wildfire. Ventura's agriculture industry suffered at least $171 million in losses due to the Thomas Fire.